1. Field of the Invention
This invention relates to a plasma, chemical vapor deposition (CVD) apparatus which may be used for various treatments such as etching a substrate to be treated, forming a vapor-deposited or deposited film, removing residual matters of a vapor-deposited or deposited film and the like in plasma atmospheres of fluorine compound gases formed in a vacuum chamber, and more particularly, to a plasma CVD apparatus suitable for forming deposited films of silicon or silicon compounds.
2. Description of the Prior Art
As a construction material for vacuum chambers, a material which surface is chemically and thermally stable and which releases gases as little as possible is desired. This is also the case for plasma CVD apparatuses, and stainless steels are used for the vacuum chambers and internal jigs such as high frequency electrode and the like. However, when the plasma CVD apparatuses comprising stainless steels are used for manufacturing semiconductor circuits using fluorine compound gases such as CF.sub.4 and the like to etch silicon wafers, or removing residual matters of deposited films, the surface of the stainless steel construction members exposed to the plasma atmosphere is corroded with fluorine radicals formed in the plasma resulting in the formation of milky white powder-like iron trifluoride (FeF.sub.3) on the surface. The FeF.sub.3 is formed by the chemical reaction of fluorine radicals with iron as a main component of stainless steel on the surface of the stainless steel. As a result, the stainless steel construction members are deteriorated and the reaction chamber is contaminated with fluorine.
In addition, the FeF.sub.3 formed on the surface of the stainless steel construction members are so fragile that the FeF.sub.3 is peeled off from the surface and suspended in the reaction chamber, and therefore, after the etching, pinholes are disadvantageously formed in the resulting deposited film. In order to solve the above-mentioned problems, it is necessary to select a material which is not easily corroded with fluorine radicals and the like. Examples of such material are nickel, chromium, gold, silver and the like, but these are so expensive and the mechanical strength is so weak that these materials are applied to the surface of stainless steel or iron by vapor deposition or the like. However, even if such metal film is formed on the surface of stainless steel or iron, the metal film is sometimes mechanically peeled off, or when the plasma discharging power of the fluorine compound gas is increased so as to produce a sufficient etching speed, the metal film is sputtered resulting in exposing the foundation material to the plasma atmosphere again, and corrosion starts at the exposed portion resulting in easy exfoliation of the metal film.